The present invention relates to a method for manufacturing a crystalline film, and particularly to a method for growing a crystalline film of a semiconductor material such as silicon on an amorphous material such as glass or metal substrate.
Heretofore, liquid phase epitaxial, chemical vapor deposition, evaporation, sputtering, or the like methods have been known as a method for producing a crystalline film. In any of these methods, a crystalline film is grown by the use of a seed crystal. Namely, according to such a method, a single-crystal substrate is adopted as substrate, and it is required to coincide the lattice constant of a crystal to be grown with that of the single crystal of the aforesaid substrate in order to obtain a favorable crystalline film.
However, if it is possible to grow a crystalline film with a good quality on an amorphous substrate such as glass or the like, it is apparent that inexpensive solar cells, panel displays of large area, or the like can be manufactured.
Graphoepitaxy method has been known as a method for growing silicon single crystal on an amorphous substrate (see M. W. Geis, D. C. Flanders and H. I. Smith, "Applied Physics Letters", vol. 35, page 71 (1979)) in which a relief having a depth of about 100 nm with a period of 3 .mu.m is fabricated on an insulating amorphous substrate in the form of grating. Amorphous silicon is deposited thereon in accordance with chemical vapor deposition (CVD) method, and then the amorphous silicon is crystallized in accordance with laser anneal method. Here, the crystal orientation in case of the crystallization is controlled by means of the relief formed on the substrate.
However, the above graphoepitaxy method has such a disadvantage in that when laser output of the anneal is increased to elevate crystal quality thereof, a rectangular shape of the aforesaid relief in cross section is deformed by means of heat, and as a result, the favorable crystal cannot be obtained. Also, there is a further disadvantage in that the aforesaid method requires a cap film (SiO.sub.2 or Si.sub.3 N.sub.4) in case of the crystallization so that the process becomes complicated.
Another example of graphoepitaxy method is disclosed by M. W. Geiss et al in "Applied Physics Letters", vol. 37, page 454 (1980) in which a relief having a depth of 100 nm with a period of 1-4 .mu.m is formed on the surface of a glass substrate being an amorphous substrate, silicon is deposited on the substrate in accordance with chemical vapor deposition method, then an oxide film is grown on the surface thereof and is heated by means of a stripe heater at 1300.degree. C. for a period of 10-20 seconds, thereby to obtain a silicon crystalline film. However, this method has such disadvantages in that the oxide film must further be formed on the deposited silicon in order to obtain the crystalline film and that even a high temperature of 1300.degree. C. is required for the crystallization.
In order to eliminate the disadvantages as mentioned above, Japanese Patent Laid-open Application No. 10224/1982 has been proposed. This publication discloses a method in which a metal such as Au or the like causing eutectic reaction with silicon at a low temperature is deposited on the whole surface of a quartz substrate on which reliefs are provided to form a metallic film, and then silicon single crystal is grown on the metallic film at a low temperature.
However, according to the method of Japanese Patent Laid-open Application No. 10224/1982, it is required that the relief on the substrate is precisely worked so as to have an angle of 109.5.degree. in order to obtain the single-crystal film, because silicon has such a tendency that the silicon &lt;111&gt; is oriented in vertical direction with respect to the substrate plane.
Furthermore, while reactive sputter etching or the like technique has been utilized for working such relief as described above, it is very difficult to provide a relief having an ideal cross section, so that there is a limit for elevating the crystal quality.
Still another method has been disclosed by E. I. Givargizov et al. In "Fifth International Conference on Vapor Growth and Epitaxy", page 195 (1981) wherein a substrate is worked to form equilateral triangular cells thereon, then a gold thin film is deposited on the patterened substrate, thereafter the resulting substrate is maintained at a temperature of 950.degree.-1100.degree. C., and silicon is deposited on such the substrate in accordance with CVD method thereby to grow the crystal. However, this method has such a disadvantage in that the equilateral triangular cell has a large dimension, for instance, 10 .mu.m, plural crystal nuclei are produced at the same time in the cell so that the film after the growth comes to be polycrystalline. In addition, the above method has another disadvantage in that a temperature, for heating the substrate is comparatively high, i.e., 950.degree.-1100.degree. C., inexpensive glass such as soda-lime glass or pyrex glass is deformed at such heating temperature so that such inexpensive glass cannot be utilized in this method.
A further method has been disclosed by B. Y. Tsaur et al. in "Fifth International Conference on Vapor Growth and Epitaxy", page 199 (1981) wherein a quartz substrate is patterned with a rectangular relief, gold is evaporated thereon, then the resulting substrate is maintained so as to have an angle of 20.degree. with a raw material vapor flux, and the substrate is heated at a temperature of 300.degree.-550.degree. C. in this situation, whereby germanium is evaporated and crystallized on the substrate. However, this method has such a disadvantage in that the substrate is remarkably inclined with respect to the vapor flux, so that a good uniformity of the resulting crystalline cannot be expected.